Method of fixing lower alkyl radicals on ethylenic double bonds of terpenes



ilni'ted States Patent METHOD OF FIXING LOWER ALKYL RADICALS ON ETHYLENIC DOUBLE BONDS OF TERPENES Albert Verley, Neuilly-sur-Seine, France No Drawing. Application April 21, 1954 Serial No. 424,779

Claims priority, application France April 27, 1953 2 Claims. (Cl. 260-587) This invention relates generally to a method of fixing simple or composite alkyl radicals to ethylenic double bonds of organic molecules. It applies more especially to substances in the terpene group and, in particular, to the synthetic production of irone and its homologues, which are of high olfactory value.

According to the invention, a tertiary amine is employed as an agent for the substitution of an alkyl radical for hydrogen on an ethylenic double bond.

This method utilises the properties of nitrogen which may be trivalent or pentavalent.

It is known that the primary, secondary and tertiary amines in which nitrogen is trivalent are capable of fixing an acid radical linked with either one hydrogen atom or with an alkyl radical.

In this way, primary, secondary, tertiary and quaternary ammonium salts are obtained: but, whilst the trivalent amines are perfectly stable within the temperature limits at which the organic products are operated upon, quaternary ammonium salts on the other hand decompose easily at temperatures between 150 and 300 whilst regenerating the tertiary amines.

Thus, tetramethylammonium bromide is split up by simple distillation into trimethylamine and methyl bromide just as ammonium chloride reduced to the vapour state is a mixture of hydrochloric acid and free amrnonia.

The ammonium salts, which are exothermic, regenerate their constituents by an endothermic reaction fed by an external source of heat.

The invention is a new application of the following phenomenon: if heat is employed to promote the dissociation of a quaternary ammonium salt in the presence of an organic molecule containing certain double bonds, the acid and alkyl radicals, which break away separately from the quaternary ammonium molecule, are capable of fixing on certain double bonds, whilst at the same time the tertiary amine is regenerated.

Any tertiary amine may be employed; but pyridine and quinoline compounds are preferred.

In this case it is always one of these two bases which is regenerated, and the reagent may be employed indefinitely.

The esters with the alkyl radical to be substituted may be either esters of strong acid such as hydrochloric, hydrobromic, hydriodic or sulphuric acid but it is equally possible, and more advantageous in certain cases, to employ esters of less energetic acids such as phosphoric, boric, oxalic, malonic and acetylacetic acids.

With certain of these esters, the quaternary ammonium salts are formed transitorily when the mixture is brought to boiling, and lead finally to the appearance of the prodnot sought. Naturally, in each particular case, the most suitable ester must be chosen and, at the same time, the most suitable solvent to complete the operation. It is suflicient that this latter should not react with the pyridine .or quinoline compound.

The general method employed in accordance with the invention may be as follows:

One mixes a molecule of the product to be substituted, a molecule of the ester of the alcohol whose radical has to be substituted, and a molecule of pyridine or quinoline base.

Even if the acid is tribasic or dibasic, it will not be necessary to employ more than one molecule of pyridine or of quinoline in each case.

Next, a quantity of solvent is added to obtain a homogeneous mixture, and this mixture is boiled, with reflux cooling, for the necessary period to ensure completion of the reaction.

The uses of this method have been studied principally in relation to the derivatives of the terpene series such as citral, geraniol, rhodinol, linalool, citronellol and a-ionone.

These substances, geraniol for example, contain ethylenic double bonds of the type concerned in the present invention. In this case, it is solely the double bond at the end of the chain which reacts.

Two examples of the method of the invention are given below:

A.Preparati0n 0 methylgeraniol The following are mixed:

Grs. 1 molecule geraniol 154 1 molecule methyl sulphate 126 1 molecule pyridine 79 For methyl geraniol, the constants are as follows:

B. P. =110.5 C.

If the same reaction is repeated on citral, one obtains methyl citral which, on condensation with acetone in the presence of dilute soda, gives pure pseudoirone of which the constants are:

E12: a d =0.8967 n =1.5279

Pseudoirone cyclised by phosphoric acid in accordance with the method employed for preparing the alpha-ionone,

gives irone, constituted by a mixture of irone-alpha and irone-beta. The irone-alpha predominates in the mixture.

I have found the following constants for pure ironealpha:

R1 Rs is the most suitable for fixation of the alkyl groupings:

CH3 CH3 H2? GHOH=CHCO.CHs H;C\ 20.0113 oi (a-ionone) Cg: /C s Hi CHGH=CHCO.CH;

H1O 0.0m

Consequently, on the u-ionone containing this grouping the methyl grouping can be fixed by the mechanism as described for geraniol whereby iso-irone is obtained, the odour of which differs only slightly from that of oc-lOl'lOIlE itself and does not recall the odour of iris as does irone.

The method of operation is similar to that for methyl geraniol as described above.

In order to distinguish the substances thus obtained from those obtained by fixation of the alkyl groupings with formation of oxide esters on the alcohols and of acetals on the aldehydes, the term iro is placed before all derivatives of the class indicated above in order to 4 make it clear that these derivatives contain the groupings which are at the basis of the formation of the irone and of its homologues.

For example, iromethylgeraniol will have the formula:

CH(CH3)2 iromethylcitronellal, the formula:

OH; /H C=CCH2CHa-GH-CH2C C a CH; CH: 0

and by hydration, this last substance will give iromethylhydroxy: citronellal.

All the substances have an olfactive value superior to that of the derivatives from which they were taken, and the method according to the present invention appears to be capable of producing these on a commercial basis.

I claim:

1. A method of inserting a lower alkyl group on an ethylenic double bond in a substance selected from the group consisting of citral, geraniol, rhodinol, linalool, citronellol and a-ionone, wherein said substance is reacted with a quaternary ammonium salt formed from a lower alkyl ester and a tertiary amine, selected from the group consisting of pyridine and quinoline compounds, to cause replacement of a hydrogen atom attached to the ethylenic double bond by the alkyl radical of said ester.

2. A method as claimed in claim 1, wherein the alkyl ester is dimcthyl sulphate.

References Cited in the file of this patent Favre et al., Helv. Chim. Acta 35, 1627-36 (1952). 

1. A METHOD OF INSERTING A LOWER ALKYL GROUP ON AN ETHYLENEIC DOUBLE BOND IN A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF CITRAL, GERANIOL, RHODINOL, LINALOOL, CITRONELLOL AND A-IONONE, WHEREIN SAILD SUBSTANCE IS REACTED WITH A QUATERNARY AMMONIUM SALT FORMED FROM A LOWER ALKYL ESTER AND A TERTIARY AMINE, SELECTED FROM THE GROUP CONSISTING OF PYRIDINE AND QUINOLINE COMPOUNDS, TO CAUSE REPLACEMENT OF A HYDROGEN ATOM ATTACHED TO THE ETHYLENIC DOUBLE BOND BY THE ALKYL RADICAL OF SAID ESTER. 